The invention relates generally to data storage systems and, more particularly, to disk-based data storage systems.
Modern disk drives are achieving continuously increasing data densities within their storage media. This increase in data density, however, has increased concerns regarding data integrity. That is, as the area on the disk surface that is used to store a single bit of digital data is decreased, it becomes more challenging to reliably read and write data to the storage medium. Many users therefore resort to techniques, such as performing periodic tape backups, to insure reliable data storage and reproduction. These techniques, however, are often very time-consuming and expensive to implement.
Therefore, there is a need for a method and apparatus that is capable of increasing the reliability of data storage and reproduction in a high capacity disk drive. Preferably, the method and apparatus will be transparent to users of the disk drive and will require no additional effort on the part of the user to achieve the reliability benefits.
The present invention relates to a data storage system that utilizes data mirroring within a single disk drive to provide enhanced data storage reliability. The principles of the invention can be implemented in drives having a single disk and also in drives using a multi-disk stack. Because each piece of user data is stored at two or more locations within the disk drive, concerns about data loss or corruption are significantly reduced. That is, even if data stored at one location has been defectively written or becomes corrupted after it has been written, the same data will normally be available at the mirror location for delivery to an attached host. In accordance with the invention, the data mirroring is preferably performed using two (or more) different disk surfaces within the disk drive. Thus, if a problem develops in the transducer/disk interface of one disk surface (e.g., a read transducer fails), the same data is still available from the other disk surface(s).
In one embodiment, the disk surfaces within the disk drive are each divided into a plurality of different regions (e.g., two regions, X and Y) and each region on a particular disk surface is aligned with the same region on the other disk surface(s) within the drive. Data from one region (e.g., region X) on one disk surface is then mirrored within at least one different region (e.g., region Y) on another disk surface. Preferably, all mirrored data will be stored within the same cylinder of the disk drive. Fixed relationships are established in the disk drive between groups of regions that mirror one another in the drive (i.e., mirror groups). Preferably, the mirrored regions within the disk drive will occur 360/N degrees from one another (with respect to the disk axis of rotation) within the drive, where N is the number of regions on each disk surface. For example, in an embodiment where each disk surface is separated into two regions X and Y, a mirrored pair will always include one X region and one Y region which are 360/2 or 180 degrees out of phase and on different disk surfaces. In an embodiment having three regions on each disk surface, X, Y, and Z, the mirrored pairs will each be 360/3 or 120 degrees apart on different surfaces.
Because each block of data is stored in at least two different locations within the drive, and these two different locations occur at different circumferential positions about the disk(s) and within the same cylinder, an effective increase in the rotational speed of the platter can be achieved during read operations. For example, in a drive that uses two regions per disk surface, the same block of data can be read by either of two paired heads every 180 degrees of rotation of the disk platter. Thus, latency is reduced and the rotational speed of the platter is effectively doubled. This technique can also be extended to simulate a 3xc3x97, 4xc3x97, or greater increase in effective rotational velocity by adding additional mirrored regions to the data configuration.